As terminals, there are an insulating connector, an insulating terminal, a feed-through, a hermetic terminal, and the like. Japanese Patent Laying-Open No. 2015-191748 (PTD 1) discloses a hermetic terminal as an example. The hermetic terminal disclosed in PTD 1 is configured such that a lead is inserted through an insertion hole of a metal outer ring and sealed with an insulating material.
A hermetic terminal is used when a current is supplied to an electrical device or an element housed inside an airtight container, or when a signal is derived from the electrical device or the element to the outside. In particular, a GTMS (Glass-to-Metal-Seal)-type airtight terminal having a metal outer ring and a lead sealed with insulating glass is roughly classified into two types including a matched sealing-type and a compression sealing-type.
In order to ensure the sealing reliability, it is important to appropriately select materials such that the thermal expansion coefficient of the metal material for the outer ring and the lead matches the thermal expansion coefficient of insulating glass. The insulating glass for sealing is determined by raw materials, required temperature profiles and thermal expansion coefficients of the metal outer ring and the lead.
In the case of matched sealing, the raw material for sealing is selected such that the thermal expansion coefficients of the metal material and the insulating glass match each other as much as possible. In order to ensure the airtight reliability and the electrical insulation properties, the matched sealing-type airtight terminal is generally configured such that a Kovar alloy (54% of Fe, 28% of Ni, 18% of Co) having the same thermal expansion coefficient as that of the glass material in a wide temperature range is used for the metal outer ring and the lead material, which are then sealed with insulating glass such as borosilicate glass.
Conventionally, these terminals may be attached to the opening periphery of a housing with a joining member such as a wax material or solder. Particularly when metal materials allowing easy formation of a passivation film made of a surface compound such as an oxide film, for example, an aluminum alloy and stainless steel, are used as materials of the housing, a special wax material containing a reducing element or flux with strong activity needs to be used in a non-oxidizing atmosphere in order to join the terminal.